1. Field of the Invention
The subject invention is directed to a screw feeder for particulate materials.
2. Description of the Prior Art
Many manufacturing processes, such as processes performed in the chemical, pharmaceutical or food industries utilize particulate materials. The particulates may take the form of pellets, flakes, powders or fibers. Efficiency in the manufacturing process requires delivery of these particulates with speed and accuracy.
Particulates present unique product delivery problems that have been considered in industry for many years. More specifically, particulates may interfere with one another and prevent a pure gravitational flow comparable to the gravitational flow of liquids. Screw feeders can transport articulate materials horizontally. However, the rate of flow of particulates through a screw feeder is affected by the rate of flow of particulates into the screw feeder. The prior art includes particular feeders that rely upon vibration to achieve a continuous and accurate flow of the particulates. The vibration causes the separate particles to move relative to one another. This movement substantially prevents or minimizes interference between adjacent particles, and thereby ensures a continuous flow of the particulates.
Manufacturing facilities often change the product being manufactured. These changes can affect the particulate feed system. For example, the required feed rate of the particulates may change. In other situations the particulate itself may be changed. Thus a feeder may be required to deliver pellets at a first feed rate on one day and then may be required to deliver a different particulate at a different rate on the next day. A good quality feed apparatus must be capable of making this transition easily and effectively. Additionally, the feed machines often have to be carefully cleaned between changes from one particulate material to another. For these reasons, it is desirable to provide a feed apparatus that can be disassembled and reassembled quickly and easily to accommodate changes from one particulate to another and to effectively clean the apparatus during those changes.
Many manufacturing processees require a specified weight of a particulate material. The prior art includes a vibratory screw batch feeders. The prior art vibratory screw batch feeder employs the above-described vibrating screw technology to achieve a very efficient flow of particulate materials. Upon delivery of a specified amount of the particulate material, the operation of the feeder is terminated. The particulate material then is moved from the feeder for use in the manufacturing process. Very effective prior art vibratory screw batch feeders operate on a loss-in-weight principle. More particularly, a weighing device is incorporated into the base of the prior art vibratory screw feeder. A sufficient amount of particulate material is placed in the hopper of the feeder. The feeder then is operated, and the weighing apparatus functions to monitor the loss in weight. When the loss in weight equals the specified batch weight, the operation of the vibratory screw feeder is terminated.
A lighter weight feeder can improve the accuracy of loss-in-weight systems. More particularly, a lighter weight feeder will result in a larger proportion of the weight sensed by the scale system being devoted to the weighing of the particulate material. Conversely, a smaller proportion of the sensed weight will be devoted to the light weight feeder. It has been determined by the inventors herein that weighing accuracy can be increased by employing a scale system dedicated more to weighing the material being processed and less to weighing the feed apparatus. A lighter weight feeder also can reduce initial delivery costs and can simplify movement of the feeder at the manufacturing facility.
Government regulations define allowable noise levels in many manufacturing work places. Accordingly, there are advantages to reducing noise produced by any apparatus, including a vibratory screw feed apparatus. Government regulations also specify materials that can be used for various food grade processing applications. In this regard, prior art feeders intended for food grade applications generally cannot be formed from the standard carbon steel that is acceptable for most other applications. Manufacturers of prior art feeders typically have resorted to stainless steel to meet government regulations for food grade applications. Stainless steel feeders typically cost about one-third more than the comparable feeder formed from conventional carbon steel.
A very effective feeder with a wide range of feeding applications is manufactured by Vibra Screw Inc. of Totowa, N.J. under the trademark Versifeeder. The Versifeeder includes a trapezoidally configured metal hopper having a large open top end and small open bottom end. The bottom end of the hopper is removably mounted to a metal trough. A vibratory apparatus is mounted externally of the trough and vibrates the trough and the hopper sufficiently to ensure a continuous gravitational flow of particulate material from the hopper into the trough. A screw feeder is rotatably mounted in the lower portion of the trough and is operative to deliver the particulate material from the trough to an external receptacle.
Despite the commercial acceptance of the Versifeeder, it is desired to make a feed apparatus that is less costly and lighter weight. It also is desired to provide a feed apparatus that very effectively delivers vibrations to the trough and hopper without significantly adding to noise within the work place. It also would be desirable to provide a lighter weight feeder for loss-in-weight batch feeding operations so that the greater proportion of the sensed weight is devoted to the particulate material being fed, thereby increasing accuracy.